Exostructure to assist in accurate syringe injection

ABSTRACT

A syringe exostructure includes a main body which removably receives a syringe having a syringe barrel and a syringe plunger. A drive plunger is reciprocatably mounted on the main body, and a plunger bar is slidably received in an axial channel on the drive plunger. The plunger bar is configured to removably couple to the syringe plunger when the syringe is introduced into the main body. A drive pawl assembly is fixed to an upper surface of the drive plunger and transfers forward motion of the drive plunger to the plunger bar as the drive plunger is advanced and disengages from the plunger bar when the drive plunger is retracted. A locking pawl assembly is fixed to the main body and extends through a slot formed in the bottom of the axial channel in the drive plunger. The locking pawl engages the plunger bar and allows the plunger bar to be advanced by the drive plunger as the drive plunger is advanced but prevents the plunger bar from being retracted by the drive plunger as the drive plunger is retracted.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation-in-part of application Ser.No. 16/035,408, filed on Jul. 13, 2018, which claims the benefit ofprovisional application No. 62/548,640, filed on Aug. 22, 2017, the fulldisclosures of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates generally to the field of medical devicesand methods. More specifically, the invention described herein relatesto devices and methods for delivering doses of a medicament from asyringe to a patient.

Existing syringes utilize a plunger to push fluids out of a barrelthrough a needle and into an injection site. In the normal clinicalsetting, the practitioner's dominant free hand deploys the syringe withthe thumb used to depress the plunger and the index and middle fingersplaced on the flanges to provide direction and stabilization. Using thestandard free-hand injection method, existing disposable syringesfunction well at delivering the total volume of the barrel as a singlemeasured dose. However, a number of clinical interventions (e.g.,botulinum toxin, deoxycholic acid, and hyaluronic acid) require that thecontents of the syringe be apportioned reproducibly in separate,discrete units (i.e., doses) across multiple injection sites during thesame procedure.

Free-hand injection is an inaccurate and imprecise technique fordelivering discrete units at multiple sites during the same procedurewith expediency. This practice carries a risk of administering anincorrect dose to an injection site, even for an experienced medicalprofessional. The risk of administering an incorrect dose utilizing thesame syringe can be due to several factors that include the change inthumb force on the plunger required to reproducibly extrude the samevolume of a fluid from a syringe as well as measurement errors whenattempting to visualize the barrel markings at different angles.

Therefore, a need exists for apparatus and methods for administeringaccurate volumetric units from a syringe filled with a medicament volumesufficient for multiple dosages.

2. Description of the Background Art

Background patents and publications include US2015025502; U.S. Pat. Nos.4,415,101; 4,022,207; and 2,491,978.

SUMMARY OF THE INVENTION

The present invention provides a syringe exostructure intended toreceive a conventional syringe and needle assembly which is eitherpre-filled or adapted to be filled with a medicament, such as but notlimited to botulinum toxin, deoxycholic acid, and hyaluronic acid, to bedelivered to a patient in multiple, sequential small aliquots or doses,usually having a volume in a range from 0.01 ml to 0.1 ml, typicallyfrom 0.025 ml to 0.05 ml. A total number of small aliquots or doses maybe in the range from 10 to 100, typically from 20 to 40, and the syringemay carry a total volume of medicament in the range from 0.3 ml to 10.0ml.

In a first aspect, the present invention comprises a syringeexostructure comprising a main body, a drive plunger, a plunger bar, adrive pawl, and a locking pawl. The main body has an upper end and alower end, and is configured to removably receive a syringe having asyringe barrel and a syringe plunger. The syringe will typically bepre-filled with a selected medicament, and the drive plunger isreciprocatably mounted on the main body. The plunger bar is slidablymounted relative to the drive plunger and has an upper end configured toremovably couple to the syringe plunger when the syringe is received onthe main body. The drive pawl is disposed at a lower end of the driveplunger and is configured to engage the plunger bar to transfer downwardmotion to the plunger bar as the drive plunger is advanced downwardly.The drive pawl will be further configured to disengage from the plungerbar as the drive plunger is retracted upwardly. This allows the driveplunger to incrementally advance the plunger bar to deliver pre-selecteddoses of the medicament from the syringe, as will be described ingreater detail below. The locking pawl is fixed relative to the mainbody and is configured to engage the plunger bar in such a way thatpermits the plunger bar to be advanced downwardly by the drive plungeras the drive plungers advance downwardly, but prevent the plunger barfrom being retracted upwardly by the drive plunger as the drive plungeris retracted upwardly.

In specific embodiments, the plunger bar has a toothed ratchet surfacewhich is engaged by both the drive pawl and the locking pawl. In suchinstances, the locking pawl is preferably formed as a living hingecoupled to the main body and oriented relative to the toothed ratchetsurface to allow downward movement of the plunger bar relative to themain body while preventing upward movement of the plunger bar relativeto the main body. Similarly, the drive pawl may be formed as a livinghinge at a lower end of the drive plunger and will typically be orientedrelative to the toothed ratchet surface so as to cause downward movementof the plunger bar relative to the main body when the drive plunger isdepressed, typically by a user's thumb. The drive pawl disengages fromthe toothed ratchet surface as the drive plunger is raised relative tothe main body (typically by a return spring), while the plunger bar isheld in place by the locking pawl.

In alternate embodiments, as in more detail below, the drive pawl maycomprise an assembly of a pair of pawls forming a cam mechanismpivotally attached to the drive plunger and having tips configured toengage opposed inner surfaces of a channel formed in the bottom of theplunger bar. Typically, the tip of each pawl of the drive pawl assemblycomprises a toothed surface configured to engage a smooth, roughened, ortoothed surface formed on the inner surfaces of the channel formed inthe bottom of the plunger bar. The toothed surface on each pawl willengage the inner surfaces of the channel as the drive plunger isadvanced and will disengage from the inner surfaces of the channel asthe drive plunger is retracted.

In still further specific instances, the plunger bar may be slidablyreceived in an axial channel formed on the drive plunger. The lockingpawl may extend through a slot, window, or other aperture formed in theaxial channel of the drive plunger, and the main body may comprise a topshell having an upper surface with a barrel groove for removablyreceiving the syringe barrel and a bottom shell having an upper surfacewhich carries the locking pawl assembly. Still further, the main bodymay comprise a T-handle fixed to the main body with a slot or otherreceptacle for receiving a plunger shaft on the syringe.

In further aspects of the present invention, a method for deliveringmultiple doses of a medicament from a pre-filled syringe comprisesattaching the pre-filled syringe to a syringe exostructure to couple aplunger button of the pre-filled syringe to a plunger bar. A driveplunger may be depressed downwardly to cause the plunger bar to advancedownwardly by a pre-determined distance to, in turn, cause the plungerbutton to advance downwardly to dispense a pre-determined dose of themedicament from the syringe. After delivering the dose, the driveplunger will be retracted upwardly (typically by a return spring) whilethe plunger bar is immobilized relative to the syringe exostructure.Multiple, successive doses are delivered by repeating the second andthird steps described above to deliver additional pre-determined dosesof the medicament from the syringe.

In specific instances of these methods, the drive plunger may be coupledto a toothed ratchet surface on the plunger bar by a drive pawl. Theplunger bar may be further immobilized by a locking pawl fixed to thesyringe exostructure, where the locking pawl engages the toothed ratchetsurface on the plunger bar to allow the plunger bar to advancedownwardly relative to the syringe exostructure and prevent the plungerbar from moving upwardly relative to the syringe exostructure.

In further exemplary embodiments, the syringe exostructure comprises amain body configured to removably receive a syringe having a syringebarrel and a syringe plunger. A drive plunger is reciprocatably mountedon the main body, and a plunger bar is slidably received in an axialchannel on the drive plunger. The drive plunger is configured toremovably couple to the syringe plunger when the syringe is introducedinto the main body, and a drive pawl assembly is fixed to an uppersurface of the drive plunger and is configured to transfer forwardmotion of the drive plunger to the plunger bar as the drive plunger isadvanced and is further configured to disengage from the plunger barwhen the drive plunger is retracted. A locking pawl assembly is fixed tothe main body and extends through a slot formed in a bottom of the axialchannel in the drive plunger and configured to engage the plunger barand allow the plunger bar to be unidirectionally advanced by the driveplunger as the drive plunger is advanced but prevents the plunger barfrom being retracted by the drive plunger as the drive plunger isretracted.

In additional specific embodiments of the syringe exostructure of thepresent invention, the drive pawl assembly comprises a pair of pawlsforming a cam mechanism pivotally attached to the drive plunger andhaving tips configured to engage opposed inner surfaces of a channelformed in a bottom of the plunger bar. Usually, the tip of each pawl ofthe drive pawl assembly comprises a toothed or other surface configuredto engage and drive a mating surface, typically a smooth plasticsurface, on opposed inner sides of the channel formed in the bottom ofthe plunger bar. Typically, the engagement surface on each pawl engageswith the mating surface on the inner surfaces of the channel as thedrive plunger is advanced and disengages with the surface on the innersurfaces of the channel as the drive plunger is retracted.

In further specific embodiments of the syringe exostructure of thepresent invention the main body comprises a top shell having an uppersurface with a barrel groove for removably receiving the syringe barreland a bottom shell having an upper surface which carries the lockingpawl assembly. The main body may further comprise a hinged cover forenclosing the syringe barrel when placed in the barrel groove.

In other exemplary embodiments, a syringe exostructure constructed inaccordance with the principles of the present invention may comprise amain body front having a barrel groove, a flange slot, and a plungershroud. A plunger bar comprises a plunger button mount, a set of lockingteeth, and a set of driving teeth. The plunger comprises a plunger head,a plunger spring, a set of driving pawls, a paw spring, and a fastener.A main body back comprises a locking pawl and a spring mount. The barrelgroove may be enclosed by a hinged door attached to the main body front,and the plunger button mount may be moveably positioned between theflange slot and the plunger head. The plunger shroud may be positionedbetween the flange slot and the plunger head, and the set of drivingteeth may be detachably coupled to the set of driving pawls by way ofthe pawl spring. The plunger spring may be elastically engaged to thespring mount opposite the plunger head, and the locking pawl may bedetachably coupled to the set of locking teeth.

In further exemplary embodiments, distance between the plunger head andthe plunger shroud corresponds to distance traveled by the locking pawlbetween each tooth of the set of locking teeth, and the syringeexostructure may still further comprise formed features surrounding theflange slot.

In further aspects of the present invention, systems may have any and/orall of the permutations and combinations of features as describedpreviously.

BRIEF DESCRIPTION OF THE DRAWINGS

To easily identify the discussion of any particular element or act, themost significant digit or digits in a reference number refer to thefigure number in which that element is first introduced.

FIG. 1 illustrates a first embodiment of a syringe exostructureconstructed in accordance with the principles of the present inventionshown in an exploded view.

FIG. 2 illustrates a top view of the syringe exostructure of FIG. 1.

FIG. 3 illustrates a lateral view of the syringe exostructure of FIG. 1.

FIG. 4 is a view of a proximal or “plunger” end of the syringeexostructure of FIG. 1.

FIG. 5 is a perspective view of a second, exemplary embodiment of asyringe exostructure constructed in accordance with the principles ofthe present invention.

FIG. 6 illustrates an exemplary plunger bar incorporated into theembodiment of FIG. 5.

FIG. 7 illustrates an exemplary drive plunger incorporated into theembodiment of FIG. 5.

FIG. 8 illustrates an exemplary T-handle incorporated into theembodiment of FIG. 5.

FIG. 9 illustrates an exemplary locking pawl assembly incorporated intothe embodiment of FIG. 5.

FIG. 10 illustrates an exemplary lower cap or bracket incorporated intothe embodiment of FIG. 5.

FIG. 11 is a side, sectional view of the syringe exostructure embodimentof FIG. 5.

FIG. 12 is a detailed, exploded view showing details of the drive pawland the locking pawl as they engage the plunger bar in the embodiment ofFIG. 5.

FIG. 13 is a detailed view of an upper portion of the syringeexostructure of FIG. 5 showing engagement of the plunger button of asyringe by the drive plunger.

FIGS. 14A through 14C illustrate in a step-wise fashion how the drivepawl and locking pawl advance the drive plunger in accordance with themethods of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

A syringe exostructure device to assist in the accurate delivery ofindividual units from a standard, single-use, disposable syringe filledwith multiple doses. The syringe exostructure is single-use anddisposable, and can be configured to support different syringe sizes anddosing requirements. The syringe exostructure includes formed featuresthat ergonomically replicate the impression of a standard syringe. Thesyringe exostructure retains a syringe in place while a cam mechanismadvances the syringe's plunger a set distance into the barrel to expel ameasured volume with each compression of the exoskeleton plunger.Tactile and/or audible feedback(s) are provided when the plunger iscompressed. The filled syringe is retained within a main body of thesyringe exostructure and secured in place by the formed features and ahinged door that closes permanently and is tamper proof.

The plunger button of the syringe engages a plunger bar that advances aset distance towards the flange and the barrel when the plunger iscompressed. The advancement of the plunger bar is driven by a set ofdriving pawls connected to the plunger that rake the plunger bar forwardthen disengage to return with the plunger to their starting position andreengage plunger bar closer to the plunger button. The distance traveledby the plunger head to the plunger shroud corresponds to the distancetraveled by the locking pawl between each tooth of the set of lockingteeth. During each advancement of the plunger bar, a locking pawldisengages the plunger bar and reengages when the plunger returns to thestarting position, preventing the plunger bar from reversing direction.When the contents of the syringe have been expelled, the entireexostructure with syringe intact is discarded and cannot be reused.

A syringe exostructure in one aspect includes a main body front with abarrel groove, flange slot, and a plunger shroud; a plunger bar with aplunger button mount; a set of locking teeth; and a set of drivingteeth. The plunger used with the syringe exostructure includes a plungerhead, a plunger spring, a set of driving pawls, a pawl spring, and afastener coupling: the pawl spring and the set of driving pawls to theplunger. A main body back portion of the exostructure includes a lockingpawl and a spring mount.

The barrel groove is enclosably aligned to a hinged door attached to themain body front, and the plunger button is moveably positioned betweenthe flange slot and the plunger head. The plunger shroud is positionedbetween the flange slot and the plunger head. The set of driving teethis detachably coupled to the set of driving pawls by way of the pawlspring, which is elastically engaged to the spring mount opposite theplunger head. The locking pawl is detachably coupled to the set oflocking teeth.

Referencing FIG. 1, a syringe exostructure 100 includes a door 102, ahinge pin 106, a main body front 108, a plunger bar 110, a fastener 112,a first driving pawl 114, a pawl spring 116, and a second driving pawl118. A plunger 120 includes a plunger head 134, and a main body back 122includes a locking pawl 126 and a spring mount 144. The plunger bar 110includes a plunger button mount 136. The main body front 108 includes abarrel groove 142, flange slot 138, and a plunger shroud 140.

The syringe exostructure 100 engages a standard disposable syringe 104that includes a barrel 128, a flange 130, and a plunger button 132. Thesyringe exostructure 100 delivers a highly controlled volume of fluidfrom a syringe 104 upon compression of the plunger 120. The main bodyfront 108 includes a formed cavity to receive the syringe 104. Theformed cavity includes structures for retaining the flange 130 andbarrel 128 of the syringe 104. The flange slot 138 is surrounded byprotruding structures resembling an enlarged version of the flange 130.The main body front 108 includes hinges for mounting a door 102 adjacentto the barrel of the syringe 104. The hinges of the door 102 and themain body front 108 are secured through a hinge pin 106. While securedwith the hinge pin 106, the door 102 swings to enclose the barrel 128 ofthe syringe 104 within the formed cavity of the main body front 108.

The plunger bar 110 engages the plunger button 132 of the syringe 104.The plunger bar 110, the plunger 120, and main body back 122 arecoincidently aligned along the length of the syringe 104. The plungerbar 110 is operatively coupled to the plunger 120 through a firstdriving pawl 114 and a second driving pawl 118, as well as to a mainbody back 122 through a locking pawl 126. The first driving pawl 114 andthe second driving pawl 118 are mounted to the plunger 120 through afastener 112. The first driving pawl 114 and the second driving pawl 118elastically engage the plunger bar 110 by way of a pawl spring 116. Theplunger head 134 of the plunger 120 protrudes from the main body back122. The plunger 120 is elastically coupled to the main body back 122through a plunger spring 124. The locking pawl 126 of the main body back122 traverses a slotted opening through the bottom of the plunger 120 toengage the plunger bar 110 on a side opposite the syringe 104.

During operation of the syringe exostructure 100, the plunger head 134is pushed in towards the main body back 122 until the plunger head 134is coincident with the main body back 122. Movement of the plunger head134 towards the main body back 122 extrudes the fluid from the barrel128 of the syringe 104. The extrusion occurs when the first driving pawl114 and the second driving pawl 118 move the plunger bar 110 to drivethe plunger button mount 136 towards the flange 130, pushing the plungerbutton 132 into the barrel 128. The first driving pawl 114 and thesecond driving pawl 118 drive the movement of the plunger bar 110towards the flange 130 and reposition the locking pawl 126 closer to theplunger button 132 during compression of the plunger spring 124.

When the plunger head 134 is released, the pawl spring 116 compresses,allowing the first driving pawl 114 and the second driving pawl 118 tomove up the length of the plunger bar 110 towards the plunger button 132as the plunger 120 returns to the starting position. The plunger bar 110is kept in place relative to the movement of the plunger 120 through theengagement of the locking pawl 126. The travel distance of the plungerhead 134 towards the main body back 122 is a set distance consistentwith the travel distance of the locking pawl 126 along the plunger bar110, resulting in a consistent volume extruded for each compression ofthe plunger head 134. The locking pawl 126 typically engages a toothedor “ratcheted” surface formed on the bottom of the plunger bar 110 toallow advancement of the plunger bar as the plunger is 120 is depressedand prevent retraction of the plunger bar as the plunger returns to itsinitial position. Usually, the locking pawl 126 will also provideaudible and/or tactile feedback as the toothed or ratcheted bottom ofplunger bar 120 is advanced by the plunger 110 over the locking pawl.

FIG. 2 illustrates a front view of an embodiment of a syringeexostructure 100, and shows the door 102, the main body front 108, theflange 130, the plunger button 132, the plunger head 134, the plungerbutton mount 136, the flange slot 138, and the plunger shroud 140.

FIG. 3 illustrates a lateral view of the syringe exostructure 100, andshows the door 102, the main body front 108, the main body back 122; theplunger head 134, and the flange slot 138.

FIG. 4 illustrates a top elevational view of an embodiment of thesyringe exostructure 100, showing the main body front 108, the main bodyback 122, and the plunger head 134.

A second embodiment of the syringe exostructure of the present inventionis illustrated in FIGS. 5 through 14A-14C. Referring in particular toFIGS. 5 through 11, a syringe exostructure 200 comprises a main bodyhaving a lower portion 201 a and an upper portion 202 b. A T-handle 204is secured to the main body between the upper and lower portions. Adrive plunger 206 and a plunger bar 208 are mounted in the upper portionof the main body 202 b, typically in a channel 203, as best seen in FIG.5.

The plunger bar 208 will typically have a plurality of ratchet teeth 210formed on a front surface thereof. The ratchet teeth 210 allowreciprocation of the drive plunger 206 to incrementally advance theplunger bar 208, will be described in greater detail below.

A conventional syringe S comprises a barrel BR with a syringe plunger SPand a plunger button SB. A lower end of the syringe S above needle N isheld in place by a lower cap or bracket 212 of the exoskeleton, whileflanges F on a middle portion of the syringe are held in a slot 236 inthe T-handle 204, and an upper end of the syringe is held by attachingthe plunger button SB in a slot 246 in a button mount 244 in of theplunger bar 208 as seen in FIG. 13. The syringe plunger SP passesdownwardly through a cut out 248 in the button mount 244.

Referring now to FIG. 7, the drive plunger 206 has a head 224 which ismanually depressed by the user, typically using a thumb, and a channel226 is formed in a front surface of the head for receiving the plungerbar 208, as best observed in FIGS. 12 and 13. A window 228 is formed ina lower end just of the drive plunger 206 above a drive pawl 230, wherethe structure of the window and drive pawl together form a living hinge231 as also be seen in FIG. 12.

Details of the T-handle 204 can be seen in FIG. 8. The T-handle includesa base 234 having a pair of lateral phalanges 235 at its upper end. Thebase 234 has a passage 240 which receives the main body of the syringe,as best seen in FIG. 5. A slot 236 formed in the front face of theT-handle 204 removably receives the phalange on the syringe where thesyringe plunger SP passes upwardly through the groove 238.

A locking pawl assembly 216 is illustrated in FIG. 9. The assemblyincludes a locking pawl 218 formed at its lower end and a yoke 220formed at its upper end. The locking pawl 218 is attached to the yoke bya living hinge 219 which allows pivoting or flexing of the locking pawlas forces are imparted to the pawl by the ratchet teeth 210 on theplunger bar 208, as described in more detail herein below.

Referring now to FIG. 10, the lower cap or bracket 212 comprises a ring213 which is received round the lower end of the lower portion 202 a ofthe main body. A clasp or bracket 214 is formed on its front surface toremovably receive a lower end of the syringe, as best seen in FIG. 5.

Referring now to FIG. 11, the assembly of the syringe S in the syringeexostructure 200 is shown in partial section. In particular, it can beseen that the syringe button SB is received in the button mount 244 ofthe plunger bar 208 while a lower end of the toothed ratchet surface 210of the plunger bar is engaged by the locking pawl 218 and the drive pawl230.

Referring now to FIGS. 11 and 12, the drive pawl 230 initially engages alower tooth of the toothed ratchet surface 210 when the syringe isunused and the syringe plunger has not been depressed. The locking pawl218 also engages the toothed ratchet surface 210 through a window 228formed in the drive plunger 206, and is coupled to a lower end of thedrive plunger 206 by a living hinge 231, as shown in FIG. 13. A channel203 of the upper portion 202 a of the main body receives the driveplunger 206, and, in turn, the channel 226 and the drive plungerslidably receives the plunger bar 208. The syringe plunger SP is mountedso that the plunger button SB is in the slot 244.

Referring now to FIGS. 14A through 14C, advancement of the syringeplunger SP by sequentially depressing the drive plunger head 224 will bedescribe. The drive plunger 206 and plunger bar 208 are shown in theirinitial configuration in FIG. 14A with the plunger bar fully extendedvertically, as shown in FIGS. 5 and 11. By depressing the drive plungerhead 224, the drive pawl 230 on drive plunger 206, is driven downwardlywhile engaging a lower tooth on the toothed ratchet surface 210 of theplunger bar 208. As the plunger bar 208 moves downwardly, the lockingpawl 218 displaces rightwardly (relative to the images in FIGS. 14A-14C)and allows the adjacent tooth to pass downwardly past the locking pawl.After the drive plunger 206 has been fully depressed, the plunger bar208 is in the configuration shown in FIG. 14, with the syringe plungerhaving been correspondingly depressed to dispense a dose of themedicament. After full depression of the driver plunger 206, spring 252will cause the drive plunger to move back upwardly, as shown in FIG.14C. Engagement of the locking pawl 218 against the adjacent tooth onthe ratchet teeth surface 210 will immobilize the plunger bar 208 sothat the plunger bar stays in place as the drive plunger moves upwardlyback to its initial position. The drive pawl 230 will displacerightwardly as the adjacent tooth moves upwardly in a conventionalratcheting motion. As shown in FIG. 14C, the plunger bar 208 is nowdisplaced downwardly by a notch relative to its initial position asshown in FIG. 14A. Depressing the drive plunger 206 can be repeated tosequentially depress the plunger bar 208 in order to deliver multipledoses of the medicament until the plunger bar 208 is fully extended andthe medicament fully delivered from the syringe.

The foregoing examples are not intended to limit the scope of theinvention. All modifications, equivalents and alternatives are withinthe scope of the invention.

What is claimed is:
 1. A syringe exostructure comprising: a main bodyhaving an upper end and a lower end and being configured to removablyreceive a syringe having a syringe barrel and a syringe plunger; a driveplunger reciprocatably mounted on the main body; a plunger bar slidablyreceived in an axial channel on the drive plunger and having an upperend configured to removably couple to the syringe plunger when thesyringe is received on the main body; a drive pawl at a lower end of thedrive plunger, said drive pawl configured engage the plunger bar totransfer downward motion to the plunger bar as the drive plunger isadvanced downwardly and to disengage from the plunger bar as the driveplunger is retracted upwardly; and a locking pawl fixed relative to themain body and configured to engage the plunger bar and to allow theplunger bar to be advanced downwardly by the drive plunger as the driveplunger is advanced downwardly but to prevent the plunger bar from beingretracted upwardly by the drive plunger as the drive plunger isretracted upwardly, wherein the locking pawl extends through a slotformed in the axial channel of the drive plunger.
 2. A syringeexostructure as in claim 1, wherein the plunger bar has a toothedratchet surface which is engaged by both the drive pawl and the lockingpawl.
 3. A syringe exostructure as in claim 2, wherein the locking pawlis formed as a living hinge coupled to the main body and orientedrelative to the toothed ratchet surface to allow downward movement ofthe plunger bar relative to the main body and prevent upward movement ofthe plunger bar relative to the main body.
 4. A syringe exostructure asin claim 3, wherein the drive pawl is formed as a living hinge at alower end of the drive plunger and is oriented relative to the toothedratchet surface to cause downward movement of the plunger bar relativeto the main body as the drive plunger is advanced and allow upwardmovement of the drive plunger relative to the main body as the plungerbar is held in place by the locking pawl.
 5. A syringe exostructure asin claim 1, wherein the drive pawl comprises an assembly of a pair ofpawls forming a cam mechanism pivotally attached to the drive plungerand having tips configured to engage opposed inner surfaces of a channelformed in a bottom of the plunger bar.
 6. A syringe exostructure as inclaim 5, wherein the tip of each pawl comprises a toothed surfaceconfigured to engage a toothed surface formed on the inner surfaces ofthe channel formed in the bottom of the plunger bar, wherein the toothedsurface on each pawl engages with the toothed surface on the innersurfaces of the channel as the drive plunger is advanced and disengageswith the toothed surface on the inner surfaces of the channel as thedrive plunger is retracted.
 7. A syringe exostructure as in claim 1,wherein the main body comprises a top shell having an upper surface witha barrel groove for removably receiving the syringe barrel and a bottomshell having an upper surface which carries the locking pawl.
 8. Asyringe exostructure as in claim 7, wherein the main body furthercomprises a T-handle fixed to the main body with a slot for receiving aplunger shaft on the syringe.
 9. A method for delivering multiple dosesof a medicament from a pre-filled syringe, said method comprising:providing a syringe exostructure as in claim 1; (a) attaching thepre-filled syringe to the syringe exostructure to couple a plungerbutton of the pre-filled syringe to the plunger bar of the syringeexostructure; (b) downwardly depressing the drive plunger on the syringeexostructure to cause the plunger bar to advance downwardly by apredetermined distance to cause the plunger button to advance downwardlyto dispense a pre-determined dose of the medicament from the pre-filledsyringe; (c) retracting the drive plunger upwardly while the lockingpawl immobilizes the plunger bar relative to the syringe exostructure;and (d) repeating steps (b) and (c) to deliver additional pre-determineddoses of the medicament from the pre-filled syringe.
 10. A method as inclaim 9, wherein the drive plunger is coupled to a toothed ratchetsurface on the plunger bar by the drive pawl coupled to the driveplunger.
 11. A method as in claim 10, wherein the locking pawl engagesthe toothed ratchet surface on the plunger bar through the axial channelon the drive plunger to allow the plunger bar to advance downwardlyrelative to the syringe exostructure and prevent the plunger bar frommoving upwardly relative to the syringe exostructure.